Circuit breakers are often used to protect wiring that carries current over external power lines (i.e., from a power source) to computer systems (i.e., loads). Such circuit breakers are effective in preventing thermal events (e.g., smoke and fire) from going beyond control. A typical circuit breaker includes a connection mechanism that can be placed in one of three positions: an off position, a set position, and a tripped position.
Suppose that such a circuit breaker is installed between external power lines and wiring that leads to a computer system. When the connection mechanism of the circuit breaker is in the off position, the circuit breaker does not allow current to flow between the external power lines and the wiring leading to the computer system. When the connection mechanism is in the set position, the circuit breaker allows current below a rated trip threshold to flow through the circuit breaker between the external power lines and the wiring. If the current flowing through the circuit breaker exceeds the rated threshold, the connection mechanism of the circuit breaker xe2x80x9ctripsxe2x80x9d, i.e., transitions from the set position to the tripped position. Once the connection mechanism of the circuit breaker transitions to the tripped position, the connection mechanism does not allow further current to flow between the external power lines and the wiring leading to the computer system in order to protect the wiring from the effects of excessive current.
In addition to the above-described conventional circuit breaker which installs between external power lines and wiring leading to a computer system (hereinafter referred to as an external circuit breaker), some computer systems include one or more circuit breakers (hereinafter referred to as internal circuit breakers) that protect circuitry within the computer systems against damage from over-current fault conditions. In general, the connection mechanism of an internal circuit breaker operates in a manner similar to that of an external circuit breaker. For example, suppose that an internal circuit breaker is installed within a computer system between a computerized device within the computer system and external wiring that leads to external power lines (perhaps through an external circuit breaker). When the connection mechanism of the internal circuit breaker is in the off position, the internal circuit breaker does not allow current to flow through it to reach the computerized device. When the connection mechanism of the internal circuit breaker is in the set position, the internal circuit breaker allows current below a rated threshold to flow through it and between the wiring leading to the external power lines and the computerized device. However, if the current flowing through the internal circuit breaker exceeds the rated threshold, the connection mechanism of the internal circuit breaker xe2x80x9ctripsxe2x80x9d, thus moving the connection mechanism.of the circuit breaker to a tripped position. Once the connection mechanism transitions to the tripped position, the connection mechanism does not allow further current to flow through it between the wiring leading to the external power lines and the computerized device thus protecting the computerized device from excessive current.
In general, the threshold of the external circuit breaker is designed to be higher than the threshold of the internal circuit breaker protecting the computerized device of the computer system since the wiring (and other external power equipment) leading to the computer system is typically designed to carry at least as much current as that which flows through circuitry within the computer system. For example, in Europe, the external circuit breaker for a computer system can have a threshold of 32 amperes, and the internal circuit breaker for the computer system can have a threshold of 30 amperes.
Some computer system installations use multiple external circuit breakers and multiple internal circuit breakers. In one configuration, the external multi-phase power equipment that protects the wiring leading from power supply lines to such a computer system includes a multi-pole or xe2x80x9cgangedxe2x80x9d multi-phase circuit breaker. The connection mechanisms for the poles (the outputs or current paths provided by the circuit breaker) share common trip linkage forcing all of the connection mechanisms to reside in the same position at the same time. For example, suppose that all connection mechanisms are in the set position. If current flowing from one of the poles exceeds the threshold for the circuit breaker, the connection mechanism for that pole transitions from a set position to a tripped position preventing further current from flowing from that pole. At the same time, the trip linkage forces the connection mechanisms for the remaining poles to automatically transition from their set positions to their tripped positions. Accordingly, when one pole of the ganged circuit breaker trips, all of the poles of the ganged circuit breaker trip thus preventing any current from flowing through the ganged circuit breaker.
In contrast to the ganged external circuit breakers of the external power equipment for the computer system, multiple internal circuit breakers for the computer system are typically un-ganged. That is, the internal circuit breakers are not mechanically coupled together. Accordingly, if one internal circuit breaker trips, the other internal circuit breakers do not automatically trip. As a result, computer systems can be designed with fault tolerant power features (e.g., multiple power units) which enable the computer systems to remain powered up and operational even when one of multiple internal circuit breakers trip (e.g., when one of three internal circuit breakers that respectively protect three power units trips leaving two internal circuit breakers and two power units operational).
The above-described external and internal circuit breakers typically carry alternating current (AC). In contrast, some circuit breaker suppliers market circuit breakers designed to carry direct current (DC). In either case, circuit breaker suppliers typically rate their circuit breakers with a threshold (e.g., 1 5-amp, 30-amp, 50-amp, etc.) and a trip coil tolerance (e.g., +/xe2x88x9235%). Prior to releasing their circuit breakers into the stream of commerce, the suppliers can test their circuit breakers to confirm that their circuit breakers conform to their rated specifications.
In one testing approach, the supplier installs a circuit breaker in a test assembly, and places the connection mechanism of that circuit breaker into the set position. The supplier then verifies that the circuit breaker properly allows current to pass through it by providing, through the circuit breaker, a test current (e.g., from a signal generator, a transformer, etc.) that is lower than a rated threshold for that circuit breaker (e.g., 30 amperes). If the supplier is testing an AC circuit breaker, the supplier provides alternating current; if the supplier is testing a DC circuit breaker, the supplier provides direct current. Next, the supplier attempts to increase the current (e.g., incrementally) until the current exceeds the rated threshold. If the circuit breaker operates properly, the connection mechanism of the circuit breaker trips when the magnitude of the current is within a specified tolerance of the rated threshold (e.g., +/xe2x88x9235%), thus preventing further current from passing through the circuit breaker. If the circuit breaker does not trip within this tolerance (or if the circuit breaker tripped prematurely before the current exceeded the threshold), the supplier typically considers the circuit breaker defective and does not ship that circuit breaker. Suppliers can increase the sophistication of the tests by varying the time delays between incremental current increases and measuring time delays before the circuit breaker trips. Such data can then be plotted to provide performance curves describing the expected performance under different current conditions.
In situations in which computer system manufacturers use off-the-shelf circuit breakers from a supplier, the manufacturers generally build their computer systems with the off-the-shelf circuit breakers without testing the circuit breakers. That is, once the circuit breakers leave the supplier, the circuit breakers are not fault tested during the computer system assembly process nor during customer installation/integration in the field. Typically, once the circuit breaker leaves the supplier, the first test of the circuit breaker is during an undesired incident such as an over-current fault condition by a power unit in the computer system. If the circuit breaker is defective, the circuit breaker does not trip or trips prematurely. Both events are undesirable particularly since manufacturers typically do not provide circuit breaker redundancy as a fault tolerant feature. The above-described situation is typical even for expensive circuit breakers which provide for electromechanical alignment before sealing and packaging the finished goods assembly.
In some situations the internal circuit breakers of some computer systems may inadvertently have thresholds that exceed the thresholds of the external circuit breakers which protect wiring that carries current between power supply lines and the computer system. For example, suppose that external power equipment at a computer system installation includes a three-pole, 32-amp, ganged external circuit breaker for protecting wiring that leads to a particular computer system (32-amps is a standard threshold for a class of external circuit breakers in Europe). A different alternating current power signal flows through each of the three poles of the circuit breaker (each power signal generally being 120 degrees out of phase with the other two power signals). Further suppose, by way of example only, that the computer system includes three internal 30-amp circuit breakers that lead to respective power units of the computer system (i.e., respective AC/DC converters, power supplies, etc.). Based on these specifications, the actual threshold of the external circuit breaker (32-amps) should be higher than the actual threshold of each internal circuit breaker (30-amps). Accordingly, in the event of an over-current fault problem in one of the power units of the computer system, one would expect the internal circuit breaker for that power unit to trip preventing further current from flowing through that power unit. If the computer system is designed to remain powered up and running upon the occurrence of such an event, the other internal circuit breakers and the external circuit breakers will not trip thus allowing the remaining power units and the computer system to continue operating.
It is possible, however, that the external ganged circuit breaker has a lower actual threshold than the internal circuit breakers. For example, suppose that both the external, ganged, 32-amp circuit breaker and the internal 30-amp circuit breakers are guaranteed to trip at 125% of their rated value +/xe2x88x9210% due to extraneous factors such as environmental conditions (temperature, etc.). Further suppose that a situation arises in which the external 32-amp circuit breaker operates at its worst case (e.g., due to a location in a poor environment) but the internal 30-amp circuit breaker operates under nominal conditions (e.g., due to a location in a proper environment).
In the above-described situation the external circuit breaker trips at t 115% of its rated value (i.e., at 125% less 10% due to the poor environmental conditions). Accordingly, the external 32-amp circuit breaker has an actual threshold of 36.8 amperes (115% of 32 amperes). Furthermore, the internal 30-amp circuit breaker trips at 125% since there are no detrimental environmental conditions that affect the circuit breaker""s operation. Accordingly, the internal 30-amp circuit breaker has an actual threshold of 37.5 amperes (125% of 30 amperes). Since, in this situation, the actual threshold of the internal circuit breaker is 37.5 amperes and the actual threshold of the external circuit breaker is 36.8 amperes, and all other variables being equal, the external circuit breaker will trip first rather than the internal circuit breaker in response to an over-current fault condition. It should be understood that 100% to 125% is a xe2x80x9cbandxe2x80x9d of uncertainty where circuit breaker tripping is not guaranteed by the supplier (i.e., the manufacturer of the circuit breaker component). This band may be of no practical use for stiff current (catastrophic) faults (i.e., when the magnitude of the current is at least 10 times higher over nominal).
Tripping of the external circuit breaker deprives the entire computer system of current since the external circuit breakers are ganged together through a common trip linkage. Accordingly, such a trip causes the computer system to perform a fail safe shutdown procedure or worse (e.g., a crash) rather than remain operational (even if the computer system is equipped with redundant power units for fault tolerance). A crash of a computer system is generally perceived as a catastrophic failure since the computer system can sustain damage when abruptly powered down in an uncontrolled state. For example, data stored in volatile memory (e.g., semiconductor memory) that is unsynchronized with non-volatile memory (e.g., disk memory) will be lost. Additionally, disk memory can become corrupt (e.g., due to inadvertent contact between a disk head and a magnetic disk of a disk drive when power is lost). Furthermore, circuitry can be damaged (e.g., due to signals passing through particular circuits in an uncontrolled manner, while the circuitry is in an undetermined state, etc.).
The invention is directed to techniques for characterizing a circuit breaker device (or electromagnetic mechanical interrupting device) that protects against extreme electrical stresses (e.g., over-current fault conditions, thermal events, etc.). Such characterization enables self-testing of circuit breakers. Manufacturers can then build computer systems with more assurance that an internal circuit breaker will trip rather than an external circuit breaker in response to an over-current fault condition within the computer system. Accordingly, computer systems equipped to continue operating even when one power unit is lost (e.g., fault tolerant computer systems with multiple power units protected by respective internal circuit breakers) can avoid catastrophic failures (e.g., a computer system crash).
Furthermore, such circuit breaker characterization enables suppliers and manufacturers to group circuit breaker devices so that all of the circuit breaker devices for particular computer system have similar actual thresholds. Such use of similar actual thresholds reduces service and repair time and costs. For example, if a technician has no knowledge of whether internal circuit breakers have similar thresholds, the technician may be unsure whether a reoccurring trip of an internal circuit breaker is due to an overly sensitive internal circuit breaker or a defective power unit, and thus may spend additional time and effort identifying and correcting the cause of the reoccurring trip. However, if the technician knows that the internal circuit breakers have similar thresholds (perhaps the technician can even use a self-test built into the internal circuit breakers), the technician may be able to easily identify the true cause of the reoccurring trip (e.g., swapping power units and seeing whether the same circuit breaker trips) thus saving time and effort.
One arrangement of the invention is directed to an apparatus for characterizing a circuit breaker device. The apparatus includes an interface that is capable of connecting to the circuit breaker device, an energy storage device that is capable of storing and releasing a particular amount of energy, and a controller that is coupled to the energy storage device and the interface. The controller (i) disconnects the energy storage device from the interface and connects the energy storage device to an external power source to store the particular amount of energy in the energy storage device, and (ii) disconnects the energy storage device from the external power source and connects the energy storage device to the interface such that, when the circuit breaker device is connected to the interface, energy is released from the energy storage device through the interface and through the circuit breaker device. The circuit breaker device is deemed as belonging to a first category when the circuit breaker device trips in response to the released energy, and deemed as belonging to a second category when the circuit breaker device does not trip in response to the released energy.
The above-described arrangement provides a simple technique for screen matching circuit breaker devices according to their actual thresholds (i.e., using the characterization apparatus to characterize multiple circuit breaker devices such as in groups of 2, 3, 4, etc. per application). Accordingly, such screening enables computer system manufacturers to build computer systems having matched circuit breakers for equal loads.
In one arrangement, the apparatus is integrated in a computer system having a computerized device for performing computerized operations, and a circuit breaker device that protects the computerized device against an extreme electrical stress. This arrangement enables the circuit breaker devices of the computer system to be tested at will (e.g., periodically) to check that the circuit breaker devices operate at actual thresholds that would enable the circuit breaker devices to trip in response to an over-current fault conditions within the computer system thus avoiding tripping of any external circuit breakers protecting wiring that leads to the computer system. If the computer system includes redundancy (e.g., multiple circuit breaker devices and multiple power units), the computer system may remain operational even though an internal circuit breaker device has tripped.
In one arrangement, the energy storage device of the characterization apparatus is configured to provide direct current through the circuit breaker device when the controller of the characterization apparatus connects the energy storage device to the interface of the characterization apparatus (e.g., by discharging a charged capacitor device).
In one arrangement, the energy storage device of the characterization apparatus includes a capacitor bank for storing energy from the external power supply and releasing energy through the circuit breaker device. The capacitor bank provides a simple technique for delivering a consistent amount of energy during each use of the characterization apparatus. The energy stored and released by the capacitor bank is based on the capacitance and voltage of the capacitor bank. In particular, the same amount of energy can be stored and released by decreasing the capacitance and increasing the voltage (i.e., decreasing the capacitance by a factor of four, and doubling the voltage). Such a tradeoff between capacitance and voltage enables a user of the characterization apparatus to easily scale the capacitor bank capacity.
In one arrangement, the energy storage device of the characterization apparatus further includes a calibration device for adjusting storage capacity of the capacitor bank (e.g., by varying the voltage or capacitance of the energy storage device). Accordingly, the amount of energy that the energy storage device stores and releases is adjustable. As such, the amount of energy stored and released by the capacitor can be precisely controlled for use in characterizing circuit breaker devices having different specified thresholds.
In one arrangement, the controller of the characterization apparatus includes a manually operated switch. When the switch is manually placed in a first position, the switch disconnects the energy storage device from the interface and connects the energy storage device to the external power source. When the switch is manually placed in a second position, the switch disconnects the energy storage device from the external power source and connects the energy storage device to the interface. When the switch is manually placed in a third position, the switch disconnects the energy storage device from both the interface and the external power source. Accordingly, the switch enables an operator (e.g., a technician) to manually control operation of the characterization apparatus. In particular, placement of the switch in the third.position isolates the energy storage device from the external power source and the interface thus enabling a technician to access and service components of the characterization apparatus (e.g., hot swap a component while the computer system remains powered up and operational).
In another arrangement, the controller of the characterization apparatus includes a switch that (i) disconnects the energy storage device from the interface and connects the energy storage device to the external power source in response to a first signal, (ii) disconnects the energy storage device from the external power source and connects the energy storage device to the interface in response to a second signal, and (iii) disconnects the energy storage device from both the interface and the external power source in response to a third signal. This arrangement enables an operator to control the operation of the characterization apparatus using software in an automated manner (e.g., periodically). For example, the first, second and third signals can be commands provided to the controller of the characterization apparatus from the computerized device. As another example, the signals can be commands provided by a separate computer (e.g., a portable laptop, a remote computer through a network or telephone line connection, etc.). In particular, the third signal can be provided to isolate the energy storage device from other parts of the computer system for online repair (i.e., access and/or replacement of components while computer system remains powered up and operational).
In other arrangements the characterization apparatus is separate from the computer system. For example, the apparatus can be used by the supplier to screen or categorize multiple circuit breaker devices on an assembly line. Alternatively, the apparatus can be used by a manufacturer (e.g., an OEM) to screen or categorize circuit breaker device stock from a supplier prior to installation of the circuit breaker stock into computer systems or computerized devices. In these various arrangements, the apparatus can be used to select circuit breaker devices with similar actual thresholds to form screened groups or sets of circuit breaker devices, and to enable use of circuit breaker devices with actual thresholds that are below the thresholds of external circuit breakers to ensure that the circuit breaker devices trip in response to internal over-current fault conditions rather than the external circuit breakers.
The features of the invention, as described above, may be employed in computer systems, methods and manufacturing procedures as well as other computer-related components such as those manufactured by EMC Corporation of Hopkinton, Mass.